Bill Gross, Pimco’s co-founder and co-chief investment officer, says stock investors should think again about the age-old “buy-and-hold” investing mantra. He says consistent, annual returns are a thing of the past.

“The cult of equity is dying,” Bill Gross wrote in his August Investment Outlook. “Like a once bright green aspen turning to subtle shades of yellow then red in the Colorado fall, investors’ impressions of ‘stocks for the long run’ or any run have mellowed as well.”

Gross points out stocks have averaged a 6.6% annual gain on an inflation-adjusted basis since 1912. But he labels that rate of return as an “historical freak” that isn’t likely to be duplicated anytime soon, due to slowing economic growth around the globe.